Respiratory Gas Exchange

minute alveolar ventilation

amount of air making it to alveoli in one minute; (tidal volume - dead space)*respiration rate

hypoxia

a state of too little O2

hypercapnia

elevated concentrations of CO2

alveolar blood flow is matched to

alveolar ventilation; blood flowing past underventilated alveoli is diverted by constricting pulmonary artieries to these alveoli

respiratory quotient

amount of CO2 produced per molecule of O2 consumed; typically about 0.8 for Western diet

respiratory quotient depends on

types of substrated being metabolized (mostly diet)

how do CO2 and O2 move from capillaries to alveoli?

simple diffusion

factors influencing rate of diffusion

diffusion = (pressure gradient * surface area)/surface thickness

relationship between O2 used by tissues and O2 diffusing into blood from lungs

exactly equal; tissues extract O2 from blood, and the blood is refilled with that amount of O2 at the lungs

pO2 and pCO2 in pulmonary vein

pO2 = 100mmHg, pCO2 = 40mmHg

pO2 and pCO2 in pulmonary artery

pO2 = 40mmHg, pCO2 = 45mmHg

pO2 and pCO2 in typical tissues

pO2 = 40mmHg, pCO2 = 45mmHg

pO2 and pCO2 in alveoli

pO2 = 102mmHg, pCO2 = 40mmHg

if pO2 decreases and pCO2 increases in blood leaving an alveolus…

blood flow will be diverted from that alveolus

if pO2 in the atmosphere is 160mmHg, why is pO2 in alveoli only 102mmHg?

1) dead volume --> not all of the air reaching the alveoli is fresh 2) rapid diffusion between alveoli and pulmonary capillaries --> O2 is diffusing to capillaries faster than it diffuses into alveoli from atmosphere

3 main factors affecting O2 exchange between alveoli and blood

1) adequate perfusion of alveoli 2) O2 reaching alveoli (air composition, alveolar ventilation) 3) gas diffusion between alveoli and blood (surface area, diffusion distance)

emphysema (what is it and what factor of alveolar gas exchange does it affect)

alveoli membranes break down --> decreases surface area for diffusion

pulmonary edema (what is it and what factor of alveolar gas exchange does it affect)

accumulation of interstitial fluid --> increases diffusion distance

fibrotic lung disease (what is it and what factor of alveolar gas exchange does it affect)

thickening of alveolar membrane --> increases diffusion distance

asthma (what is it and what factor of alveolar gas exchange does it affect)

overconstriction of bronchioles --> increased airway resistance --> decreased alveolar ventilaton

describe efficiency of "refilling" of pulmonary capillaries

gas exchange to "refill" pO2 in capillaries is normally complete within the first 20% of capillary length

hemoglobin

O2-carrying protein in red blood cells

concentration of Hb in blood

150g/L or 15%

each gram of Hb can carry __mL O2

1.34mL

how is O2 distributed in blood?

98% carried by hemoglobin, 2% dissolved in plasma

Hb structure

tetramer; 2𝛼 and 2β subunits, each with their own heme group and each can carry 1 O2 --> 1 Hb can carry 4 O2

percent Hb saturation

proportion of Hb subunits bound to O2

energetics of Hb oxygenation

Hb + O2

shape of O2 binding curve

sigmoidal due to cooperative binding

regulation of Hb affinity for O2 (3 factors; how are they similar?)

1) temperature: increased temp decreases affinity 2) pH: increased acidity decreases affinity 3) 2,3-BPG: decreases affinity; similar because all are products of active tissue

bicarb equation

CO2 + H2O

how is CO2 distributed in blood?

7% dissolved in plasma, 25% binds to Hb to form carbaminohemoglobin, 70% is converted to bicarb and H+ (some H+ bind to Hb)